U.S. patent number 5,039,587 [Application Number 07/404,072] was granted by the patent office on 1991-08-13 for oxide-coated carriers and preparation and use thereof.
This patent grant is currently assigned to BASF Aktiengesellschaft. Invention is credited to Erwin Czech, Werner Ostertag, Franz-Ulrich Schmitt, Detlef Schulze-Hagenest.
United States Patent |
5,039,587 |
Czech , et al. |
August 13, 1991 |
Oxide-coated carriers and preparation and use thereof
Abstract
A novel carrier which is stable and effective over long cycle
times (6.times.10.sup.6 prints), has an iron oxide coating of the
formula (FeO).sub.x.Fe.sub.2 O.sub.3 where x=0.1-1 and is obtained
by treating steel cores (or balls) with defined small amounts of
sulfuric acid of defined concentration, partial oxidation of the
cores thus treated and drying at 60.degree.-150.degree. C. at
.ltoreq.100 mbar.
Inventors: |
Czech; Erwin (Biblis,
DE), Ostertag; Werner (Gruenstadt, DE),
Schulze-Hagenest; Detlef (Grasbrunn, DE), Schmitt;
Franz-Ulrich (Gerlingen, DE) |
Assignee: |
BASF Aktiengesellschaft
(Ludwigshafen, DE)
|
Family
ID: |
6362846 |
Appl.
No.: |
07/404,072 |
Filed: |
September 7, 1989 |
Foreign Application Priority Data
|
|
|
|
|
Sep 13, 1988 [DE] |
|
|
3831091 |
|
Current U.S.
Class: |
430/111.34;
428/404 |
Current CPC
Class: |
G03G
9/1075 (20130101); Y10T 428/2993 (20150115) |
Current International
Class: |
G03G
9/107 (20060101); G03G 009/113 () |
Field of
Search: |
;430/108,137
;428/404 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Martin; Roland
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
We claim:
1. A carrier which has an iron oxide surface coating of the formula
(FeO).sub.x . Fe.sub.2 O.sub.3 (x=0.1-1) on steel cores and is
obtainable by treating the steel cores (or balls) with aqueous
sulfuric acid using per m.sup.2 of ball surface area from
5.times.10.sup.-5 to 2.5.times.10.sup.-4 mol of sulfuric acid, the
acid concentration at the start of the treatment being from
10.sup.-2 to 10.sup.-6 mol/l, oxidizing the balls which have been
treated with sulfuric acid with oxygen or an oxidizing agent in an
amount which corresponds to from 5.times.10.sup.-5 to
5.times.10.sup.-4 oxidation equivalent/m.sup.2 of ball surface
area, and drying the balls at from 60.degree. to 150.degree. C.
under a pressure of .ltoreq.100 mbar.
2. The carrier of claim 1, wherein the treatment with sulfuric acid
and the oxidation are carried out simultaneously.
3. The carrier of claim 1, wherein the oxidation is carried out
with atmospheric oxygen or with an alkali metal permanganate.
4. The carrier of claim 1, wherein the steel cores (or balls) have
been produced by the technique of spray atomizing.
Description
Electrophotographically produced images today are predominantly
developed with dry toners in a one-component or two-component
system. The one-component system comprises a magnetizable toner.
The developer in two-component systems customarily comprises
magnetic carrier particles and nonmagnetic toner particles.
In electrophotography, a photoconductor coupled with charge
carriers is selectively exposed to produce an invisible, latent
image. To make this charge image visible, it must be developed.
This is done by supplying a toner powder, which in the case of the
two-component system consists essentially of a coloring component
and binder and has particle sizes of from 5 to 13 .mu.m. The toner
powder is transported to the photoconductor via the magnetic brush,
i.e. chains of carrier aligning with the electrical field lines
along a sector magnet. The carrier, which carries the toner, is
uniformly supplied to the photoconductor. This transport produces a
controlled, electrostatic charge on the toner powder which can then
be transferred to the photoconductor. Excess toner is brushed off
the photoconducting layer by the carrier magnetic brush and
conveyed back into the reservoir vessel. The developed toner image
is then transferred to paper and fixed. The principle of the
development process using two-component systems is well known, and
described in detail for example in DE-C 2,404,982.
The carrier typically has a core whose material is magnetizable.
The material can be made for example from iron, nickel, magnetite,
.gamma.-Fe.sub.2 O.sub.3 or certain ferrites. Steel carriers,
having excellent soft magnetic properties, are likewise still much
in use today.
To instill the electrical and electrostatic properties required,
the carrier particles usually carry a surface coating. This
overcoat also has an effect on the mechanical properties. Spherical
particles are particularly free-flowing. Irregular carrier shapes
are used if a high electrostatic charge is desired. The toner
particles are charged to the desired extent by electron exchange
processes or alternatively ion transfers [K. L. Birkett and P.
Gregory, Dyes and Pigments 7 (1986), 341], which are mutually
induced by the friction between toner and carrier particles
(triboelectric effect). Since the toner particles are in vigorous
mechanical interaction with the carrier surface, the desired charge
exchange processes, however, are also accompanied by undesirable
side effects such as abrasion and impaction on the surface.
Abrasion occurs not only at the toner but also at the carrier
surface due to the intense frictional interaction. Minuscule
particles abraded off the toner impact on the carrier surface,
reducing carrier activity as evidenced by the continuous loss, or
exhaustion, of the ability of the carrier to charge the toner
particles to a certain level. The result is that the printed image
deteriorates.
To prevent toner impaction on the carrier surface, it was customary
in the past to use plastics having low surface energies, for
example silicone resins (e.g. U.S. Pat. No. 3,562,533), or
hydrofluorocarbon-containing polymers (e.g. U.S. Pat. No.
3,533,835). The mechanical stability of such carrier coatings
nonetheless left something to be desired. There was therefore a
general shift toward improving the abrasion resistance by means of
fillers such as silicon carbide, potassium titanate (DE-A
3,312,741), chromium oxide or iron oxide (U.S. Pat. No. 3,798,167),
or other metal oxide compounds. Because most polymers have an
excessively high electrical resistance it was also necessary to add
conductive components. Although this measure ensures that the
surface is mechanically stable, the toner particles abrade in the
course of transportation, generating detritus which goes on to the
surface of the carrier, becoming compacted thereon and as a result
reducing the activity of the carrier. To eliminate this
disadvantage, it has been attempted to make good the decreasing
activity of the carrier by means of a coating which contains for
example organotin compounds with concentration gradients within the
layer (DE-A 3,511,171). This layer acts as a catalyst in the curing
of the silicone resin and in a way makes good the loss of carrier
activity incurred in the case of a specific toner. However, the
preparation of such layers is only possible by a complex process
and must be adapted to the viscoelastic characteristics of the
toner in question.
Fundamental studies concerning exhaustion and triboelectricity have
been carried out. In these studies, the phenomenon of toner
impaction was investigated as a function of toner particle size,
carrier particle size, the coating on the toner and the level of
toner on the carrier (R. J. Nash and J. T. Bickmore, "Toner
impaction and triboelectric aging", Paper Summaries of the 4th
Congress on Advances in Non-Impact-Printing Technologies, p. 84,
March 1988, New Orleans). The results of these studies can be
summarized as follows: smaller toner particles, smaller carrier
particles and hydrophobic silica coatings on the toner prolong the
life of the developer.
Steel carriers having certain electrical properties are known.
According to U.S. Pat. No. 3,632,512, steel balls are anoxidized in
a defined manner by treatment with 2N sulfuric acid; according to
CA-A-1,103,079, they are oxidized by heat treatment. These carriers
have an oxide layer on their surface. The treatment of steel balls
with 2N sulfuric acid as described in U.S. Pat. No. 3,632,512 is
associated with appreciable water pollution, and industrial
implementation is difficult and expensive because of the
complicated drying. The carriers obtained by this process have very
homogeneous overcoats, they improve the charge distribution and
they ensure a better print.
The purpose of these surface treatments is to obtain very
abrasion-resistant coatings as well as good electrical properties
(average specific resistances of from 10.sup.-1 to 10.sup.-8
.OMEGA..cm.sup.-1). The decrease in carrier activity can be delayed
owing to the low affinity of the iron oxide layer for the toner
resin. Nonetheless, a continuous decrease in carrier activity is
likely since the toner resin particle detritus, owing to the
electrostatic charge, initially remains on the carrier surface and
is increasingly compacted thereon by the tumbling motion of the
carrier particles. However, the question arises whether the
phenomenon of exhaustion cannot be delayed in some fundamentally
different way.
It is a basic disadvantage of all existing carrier developers that
carrier activity continuously decreases; that is, the print is
constantly changing over the life of the developer. To prevent
this, the carrier surface must be continuously regenerated in order
to retain its original character over many thousand copying
cycles.
It is an object of the present invention to prepare steel carriers
having an oxidic surface which becomes continuously regenerated in
use, ensuring a long life of consistently high print quality.
Furthermore, the process should be inexpensive and environmentally
safe.
We have found that this object is achieved by the carrier of the
invention.
The present invention accordingly provides a carrier which has an
iron oxide surface coating of the formula (FeO).sub.x. Fe.sub.2
O.sub.3 (x=0.1-1) on steel cores and is obtainable by treating the
steel cores (or balls) with aqueous sulfuric acid using m.sup.2 of
ball surface area from 5.times.10.sup.-5 to 2.5.times.10.sup.-4 mol
of sulfuric acid, the acid concentration at the start of the
treatment being from 10.sup.-2 to 10.sup.-6 mol/l, oxidizing the
balls which have been treated with sulfuric acid with oxygen or an
oxidizing agent in an amount which corresponds to from
5.times.10.sup.-5 to 5.times.10.sup.-4 oxidation equivalent/m.sup.2
of ball surface area, and drying the balls at from 60.degree. to
150.degree. C. under a pressure of .ltoreq.100 mbar.
The carrier of the invention has a surface which conforms to the
material composition (FeO).sub.x Fe.sub.2 O.sub.3. The novel
carrier has a surface where the process of abrasion performs the
important function of cleaning and renewing the carrier particle
surface.
The surface of the carrier according to the invention comprises an
approximately 0.3 .mu.m thick, largely X-ray amorphous iron oxide
layer whose composition of (FeO).sub.x Fe.sub.2 O.sub.3, where x is
0.1.ltoreq.x.ltoreq.1 was determined by wet-chemical analysis of
collected samples of detritus. If concentration profiles were
obtained by ablating the carrier surface with argon plasma a
scanning auger microprobe was used to determine the decrease oxygen
concentration from the outside toward the inside. The results were
compared with those of carriers which have an artificially vacuum
vapor deposited iron oxide film of a defined thickness. The layer
thickness was found to be about 0.3.+-.0.1 .mu.m. Weak X-ray lines
indicate that the oxidic surface has a spinal structure.
The surface layer of the carrier of the invention consists of
intergrown, predominantly plateletlike oxidation products of the
iron surface, the platelets being on average from 0.05 to 0.1 .mu.m
in size and about 10-50 nm in thickness. The platelets are only
intergrown at the edges, so that a breaking out of individual
particles is possible under mechanical stress.
The developer composed of toner and a carrier according to the
invention can as it were be described as a three-component system
composed of toner, carrier and detritus. Using the specific coating
technique of the invention made it possible to produce an oxidic
surface layer which in the course of the copying process produces
small amounts of abrasive iron oxide particles.
The iron oxide particles 0.05-0.1 .mu.m in size emanating from the
carrier surface are initially kept as detritus on the carrier
surface by the large forces of adhesion. On the carrier surface
they can combine with the toner detritus and thus facilitate the
detachment thereof from the carrier surface.
The novel carrier is produced by subjecting the uncoated steel
carrier to specific treatment with aqueous sulfuric acid, oxidizing
and finally drying. In the acid treatment, 0.05-0.25 mmol of acid
is used per m.sup.2 of steel carrier surface area, the acid
concentration at the start of the treatment being from
1.times.10.sup.-2 to 1.times.10.sup.-6 mol/l; that is, the pH must
not be less than 2. In a particularly advantageous procedure, the
initial pH is 3.5-4.5. It was found that from 5.times.10.sup.-5 to
2.5.times.10.sup.-4 mol of sulfuric acid is required per m.sup.2 of
surface area in order to produce a surface coating of optimal
thickness. If small amounts of acid are used in the treatment, then
a small effect is observed, compared with the uncoated material, in
respect of the electrostatic charge distribution. Excessively large
amounts of acid lead to products which are not very stable to
storage: the coating is too brittle and the carrier may
corrode.
Sulfuric acid is preferred since sulfate ions do not reduce the
shelf life of the steel balls. The use of other mineral acids is
possible, but, for example in the case of hydrochloric acid, leads
to corrosion problems. If dilute nitric acid is used, the iron(II)
ions formed undergo uncontrolled oxidation.
This sulfuric acid treatment and the partial oxidation of the
Fe(II) ions may be carried out in succession or, alternatively,
simultaneously. The partial oxidation can be effected for example
with oxygen-saturated water or acid solution or alternatively by
the addition of an alkali metal permanganate in a normality of from
5.times.10.sup.-5 to 5.times.10.sup.-4 mol per m.sup.2 of surface
area. However, the oxidation can also be carried out with other
oxidizing agents such as hydrogen peroxide and ammonium
peroxodisulfate.
Preferably, the acid treatment and the oxidation are carried out
simultaneously, in particular with oxygen-saturated sulfuric acid
or permanganate-containing sulfuric acid. The oxidation of the
resulting iron(II) hydroxide, however, can also be effected with
oxygen-containing gases, preferably air, after the sulfuric acid
treatment.
The amount of oxidizing agent is from 5.times.10.sup.-5 to
5.times.10.sup.-4 oxidation equivalent per m.sup.2 of steel carrier
surface. The oxide-coated carrier is dried at
60.degree.-150.degree. C. and pressures .ltoreq.100 mbar. If the
product is dried at 70.degree. C. it will change its color after a
few days. However, the effect remains the same (see Example 3).
Preference is given to carriers which are dried above 100.degree.
C. Owing to the extremely low sulfuric acid concentration, the
process is environmentally very safe.
The raw material used, i.e. the steel carrier, was for example a
steel ball product available from Metallurgica Toniolo S.p.A.,
Maerne, Italy, under the trade designation TC 100. These steel
balls consist of 98.5% of Fe, 0.4% of Mn, 0.4% of Si, 0.1% of each
of Ni, Cr and Cu, and traces of Co, Zn, Mg and Ca. However, it is
also possible to use a raw carrier material having an irregular
particle shape. Particular preference is given to steel carriers
which have been produced by spray atomizing.
The studies concerning carriers which have satisfactory performance
characteristics show that a carrier will always produce a good
print and be considered fully satisfactory if the electrostatic
chargeability of the toner particles present in the developer has a
narrow distribution (q/d). The electrostatic chargeability
distribution was measured with a q/d meter (from Epping GmbH,
Neufahrn). The method of measurement exploits the different
settling rates of toner particles having different q/d values (q:
charge on toner particle, d: diameter of a toner particle) on an
electrode in an electric field. In addition, the toner
concentration in the developer must not change; that is, the number
of toner particles on the carrier should remain substantially the
same over the period of use; it must not increase or decrease,
apart from minor variations.
The stress or lifetime test to establish whether the carrier was
fully satisfactory was carried out under realistic conditions in an
ND2 laser printer (from Siemens AG, Munich). This printer consumed
on average 350 g of toner per hour when filled with 8 kg of
developer. The specific toner consumption was accordingly 43.8 g of
toner per kg of developer per hour.
When 3 million prints had been produced, the carrier in the
developer had been in use for about 600 hours. During this time
about 210 kg of toner were consumed, i.e. 26.3 kg of toner per kg
of developer.
Even after the novel carrier present in the developer had been in
use for about 1200 hours, there were no signs of deterioration in
the print; that is, after over 6 million prints the carrier
according to the invention was still fully effective.
By comparison, a carrier prepared as described in Example 1 of U.S.
Pat. No. 3,632,512 showed distinct signs of fatigue after just 3
million prints, as evidenced by a marked deterioration in the print
and a disproportionate buildup of toner in the developer. If the
q/d distribution of the toner particles present in this exhausted
developer is determined, it is found that, compared with the toner
in the still fully functioning developer which contains the carrier
according to the invention, the charge distribution is distinctly
broader after 3 million prints.
To corroborate the novel concept of the self-regenerating carrier
surface and the important role of the detritus, an uncoated steel
carrier was admixed with finely divided, largely amorphous iron
oxide to prepare a developer.
In the initial phase (for about 6 hours) this developer performed
perfectly well in the laser printer. The print proved fully
satisfactory and, judged by the above test, the toner particles
present in the developer had a narrow charge distribution (q/d
measurement). However, with time and very plainly after the
artificially added iron oxide detritus had been removed the
developer presently became exhausted. The print deteriorated and
the toner particles in the developer had a broad charge
distribution. By analyzing for iron in the toner it was possible to
show that the developer based on the carrier of the invention forms
detritus at a uniform rate over its entire lifetime.
The invention is further illustrated by the following Examples:
EXAMPLE 1
A 1000-ml stirred vessel equipped with a pH electrode, a blade
stirrer, a sieve plate and inlet and outlet means is charged with
1000 g of steel powder (steel powder TC 100, from Toniolo, Maerne,
Italy) having a particle size distribution of 75-175 .mu.m, a
weight average particle size of 105 .mu.m and a surface area of 36
cm.sup.2 g. In a feed vessel, 4 l of a sulfuric acid solution at pH
4 is saturated with air (0.0205% by volume of O.sub.2 in water at
15.degree. C.) by introducing an air stream at 100 l/h. The
solution is then pumped at a rate of 20 l/h through the dumped
steel powder. The solution which runs off is recycled into the feed
vessel, while the pH in the feed vessel and the reactor is measured
continuously. Air is blown into the feed vessel at a rate of 100
l/h. After about 20 minutes the pH in the feed vessel has risen to
8 and no longer differs from the pH in the reaction vessel.
The slightly yellow solution is discharged from the reactor. The
reactor vessel is then connected to a vacuum pump, heated with 4
bar steam to 135.degree. C. and dried under a pressure of 55 mbar
in the course of 4 hours. The very free-flowing, slightly yellow
steel powder is then discharged from the reactor and can be used to
prepare the developer.
COMPARATIVE EXAMPLE 1
The directions of Example 1 of U.S. Pat. No. 3,632,512 were
followed to prepare a carrier from the steel balls used in Example
1. To this end, the steel balls were treated with 2N sulfuric acid,
then washed with water and methanol as described in the Example and
then IR-dried at 80.degree. C. in the presence of air.
EXAMPLE 2
A 1000-ml stirred vessel equipped with a pH electrode, a blade
stirrer, a sieve plate and inlet and outlet means is charged with
1000 g of steel powder (steel powder TC 100 from Toniolo, Maerne,
Italy) using a particle size distribution of 75-175 .mu.m, a weight
average particle size of 105 .mu.m and a surface area of 36
cm.sup.2 /g. Thereafter, 4 l of sulfuric acid solution at pH 4, in
which 1.3.times.10.sup.-5 mol/l of potassium permanganate has been
dissolved, is pumped with stirring at a rate of 20 l/h through the
dumped steel powder. The solution which runs off is recycled into
the feed vessel and the pH in the feed vessel and the reactor is
measured continuously. After about 15 minutes the pH in the feed
vessel has risen to 8 and is no longer different from the pH in the
reaction vessel.
The slightly brown solution is discharged from the reactor. The
reactor with its steel ball contents is then evacuated (55 mbar)
and heated, with the vacuum pump running, to 120.degree. C., and
the product is dried for 4 hours. Thereafter the very free-flowing,
slightly yellow steel powder is discharged from the reactor. It can
be used directly for preparing the developer.
EXAMPLE 3
A 1000-ml stirred vessel equipped with a pH electrode, a blade
stirrer, a sieve plate and inlet and outlet means is charged with
1000 g of steel powder (steel powder TC 100, from Toniolo, Maerne,
Italy) having a particle size distribution of 75-175 .mu.m, a
weight average particle size of 105 .mu.m and a surface area of 36
cm.sup.2 /g. In a feed vessel, 4 l of sulfuric acid solution of pH
3 is prepared. The solution is then pumped at a rate of 20 l/h
through the dumped steel powder. The solution which runs off is
recycled into the feed vessel, while the pH in the feed vessel and
the reactor is measured continuously. After about 17 minutes the pH
in the feed vessel has risen to 8 and is no longer different from
the pH in the reaction vessel.
The slightly yellow solution is discharged from the reactor. The
reactor is then evacuated. Thereafter, with the vacuum pump
running, 100 ml of air is passed through the moist iron powder bed
in the course of 5 minutes. The air supply is then terminated and
the moist carrier is discharged from the reaction vessel under a
nitrogen blanket. One-third portions of the moist carrier were
dried at 70.degree., 100.degree. and 130.degree. C. respectively in
an evacuable drying cabinet for 4 hours.
After cooling, the samples were conditioned at 85% relative
humidity at 25.degree. C. for 1 week.
The color of the carrier dried at 70.degree. C. changed from yellow
to a rusty red. However, the electrostatic chargeability
corresponds to that of the carrier dried at 130.degree. C. The
samples dried at 110.degree. and 130.degree. C. do not show any
color change, and the electrostatic charge distribution corresponds
to that of Example 2.
Developer 1
The developer is prepared by accurately weighing out 988 g (98.8%
by weight) of the carrier prepared as described in Example 1 and 12
g (1.2% by weight) of original toner for the ND2/ND3 Siemens laser
printer (Siemens AG, Munich) and subsequent activation. To this
end, the mixture is agitated for 5 minutes in a 500-ml glass flask
on a roll block at 60 rpm.
Developer 2
For comparison, a developer was prepared from 98.8% by weight of
the steel carrier obtained as described in Comparative Example 1
and 1.2% by weight of toner for Siemens laser printer ND2/ND3 and
activated in the same way as developer 1.
Developer 3
For comparison, a developer is prepared from 98.8% by weight of
uncoated steel balls (TC 100) and 1.2% by weight of toner for
Siemens laser printer ND2/ND3. Activation was as for developer
1.
Developer 4
An uncoated carrier (TC 100) was mixed with 0.005% by weight of a
finely divided iron oxide (Sicotrans Orange L 2515, BASF AG,
Ludwigshafen) and the mixture was shaken for 15 minutes in a red
devil. Thereafter a developer is prepared by mixing 98.8% of
carrier thus prepared and 1.2% by weight of toner for Siemens laser
printer ND2/ND3.
Determination of the Electrostatic Chargeability q/m
The activated developer (charge separation by triboelectricity) is
accurately weighed out and introduced into a measuring cell capped
at the top and the bottom with sieve inserts.
The mesh size at 50 .mu.m is such that all the toner particles can
pass through it while all the carrier (75-175 .mu.m) remains on the
inside of the measuring cell. The measuring cell, which has a
cylindrical shape, is insulated and coupled to an electrometer (q/m
meter, Epping GmbH, Neufahrn). By means of a fast air stream of
about 4000 cm.sup.3 /min and simultaneous aspiration, the toner,
which adheres electrostatically to the carrier, is completely
removed from the carrier particles and blown out of the cell. The
charge can be read off on the electrometer. The amount of charge of
opposite sign then corresponds to the charge on the blown-off
toner, the mass of which is determined by backweighing the
measuring cell. In the printer, the developer is activated in the
course of magnetic brush development by the toner particles which
glide along the carrier chains. The degree of charge separation
depends on the materials used and on the duration and intensity of
activation. Very strong vibratory movements can destroy a
developer, since either the coatings are rubbed off or the toner
impacts on the carrier surface.
Experiment 1
Determination of q/m
600 g of developer 1 are introduced into a laser printing LD tester
(from Epping, GmbH, Neufahrn near Munich). Toner for Siemens laser
printer ND2/ND3 is introduced into the reservoir vessel. The speed
of the magnetic brush is 15 cm/sec. The distance to the
photoconductor is 2.0 mm. The speed of the semiconductor drum is 7
cm/sec., and the potential between the conductor and developer roll
is 300 V. The amount of toner transferred is aspirated away on the
other side of the photoconductor. After a few minutes the process
of development is interrupted and a sample of developer 1 is taken.
A q/m measurement is carried out. The q/m measurement is found to
be 15.5.+-.1.0 .mu.C/g (Table 1).
The deviation was determined in this experiment as in the other
experiments as the arithmetic mean of 10 runs.
The q/m values of comparative developers 2, 3 and 4 were determined
by the same method. The measurements are summarized in Table 1.
Results
The average electrostatic chargeability of developer 1, 2 and 4 are
the same within the margin of error. Developer 3, which is based on
an uncoated carrier, has a very high charge compared to the other
developers.
Experiment 2
20 g of developer 1 are activated in a 50 ml glass flask on a 60
rpm roll block for 10 minutes. Then a q/d measurement (q/d meter,
Epping GmbH, Neufahrn) was carried out. The average q/d value was
6.9.+-.3.6 fC/10 .mu.m with a standard deviation of 4.0.+-.0.5. The
same method was used to carry out q/d measurements on developers 2,
3 and 4. The results are summarized in Table 1.
Experiment 3
Determination of the Amount of Toner in Developer 1 Under Operating
Conditions.
8000 g of developer 1 were introduced into an ND2 laser printer
(from Siemens AG, Munich) and operated under customary conditions.
The blackness and quality of the print were monitored. After every
500,000 prints the iron content of the toner transferred to the
paper was analyzed. A sample of the developer was taken after 3
million prints to determine the total toner concentration. It was
found to be 1.8%. After 6 million prints the developer was removed
from the machine to determine its total toner concentration. It was
found to be 3.6%.
Experiment 4
Determination of the Amount of Toner in Developer 2 Under Operating
Conditions
As in experiment 3, 8000 g of developer 2 were introduced into an
ND2 laser printer and the printer was operated as in experiment 3.
After every 500,000 prints toner samples were taken to determine
the iron content. After 3 million prints the total toner
concentration was already 5.6%.
The experiment was then discontinued.
The results are summarized in Table 2.
Experiment 5
Determination of the Amount of Toner in Developer 3 Under Operating
Conditions
Developer 3 was tested in a laser printer as described in
experiment 3. The run had to be discontinued after just a few
thousand prints because of the poor quality of print. The results
are summarized in Table 2.
Experiment 6
Determination of the Amount of Toner in Developer 4 Under Operating
Conditions
Developer 4 was tested in a laster printer as described in
experiment 3. The developer produced over 5000 clean, satisfactory
prints. Then the quality of print deteriorated dramatically, so
that the run had to be discontinued. The results are summarized in
Table 2.
TABLE I ______________________________________ Electrostatic
chargeabilities of developers Average q/m in q/d in Standard
.mu.C/g fC/10 .mu.m deviation
______________________________________ Developer 1 15.5 6.9 3.6
(according to the invention) Developer 2 16.0 7.2 4.0 (carrier
according to U.S. Pat. No. 3,632,512) Developer 3 36.5 13.9 5.9
(uncoated steel carrier) Developer 4 14 7.0 3.4 (steel carrier
coated with finely divided iron oxide)
______________________________________
TABLE 2 ______________________________________ Results of the
printing test Devel- Devel- Devel- Devel- oper oper oper oper 1 2 3
4 ______________________________________ Image quality + black-
ness by densitometric measurement of a reference sample After 1000
prints good good too good 0.48 0.47 strong 0.48 0.53 After 10,000
prints normal normal inade- inade- 0.53 0.51 quate quate -- --
After 100,000 prints normal normal -- -- 0.52 0.55 Thereafter
normal normal 0.53 0.52 Iron content in toner after 1000 prints 1.0
ppm 0.5 ppm -- 1 ppm after 500,000 prints 1.06 ppm <0.1 ppm --
-- 1 million prints 0.8 ppm <0.1 ppm -- -- 1.5 million prints
1.5 ppm <0.1 ppm -- -- 2 million prints 0.9 ppm <0.1 ppm --
-- 2.5 million prints 0.7 ppm <0.1 ppm -- -- 3 million prints
0.9 ppm <0.1 ppm -- -- 3.5 million prints 1.0 ppm <0.1 ppm --
-- 4 million prints 0.7 ppm <0.1 ppm -- -- 4.5 million prints
0.6 ppm <0.1 ppm -- -- 5 million prints 0.5 ppm <0.1 ppm --
-- 5.5 million prints 0.7 ppm <0.1 ppm -- -- 6 million prints
0.8 ppm <0.1 ppm -- -- Total toner concen- tration At the start
1.2 1.2 1.2 1.2 After 3 million prints 1.8 5.6 -- -- After 6
million prints 3.6 -- -- --
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